A micromort is a unit of risk measuring a one-in-a-million probability of death (from micro- and mortality). Micromorts can be used to measure riskiness of various day-to-day activities. A microprobability is a one-in-a million chance of some event; thus a micromort is the microprobability of death. The micromort concept was introduced by Ronald A. Howard who pioneered the modern practice of decision analysis.

An application of micromorts is measuring the value that humans place on risk: for example, one can consider the amount of money one would have to pay a person to get him or her to accept a one-in-a-million chance of death (or conversely the amount that someone might be willing to pay to avoid a one-in-a-million chance of death).

When put thus, people claim a high number but when inferred from their day-to-day actions (e.g., how much they are willing to pay for safety features on cars) a typical value is around $50 (in 2009). The average risk of dying per day can be calculated from the average lifetime. Assuming this is 70 years, that means there is one death for every 25,550 days lived (70 x 365 = 25,550). The number of micromorts per day is one million divided by that number of days; in this case, about 39 micromorts acquired individually every day. The number of micromorts per hour is divided by 24 hours; that is about 1.63 micromorts per hour. This is just an average across an entire population: the number of micromorts per day will vary across different categories of people, such as by age, sex and lifestyle.

Activities that increase the death risk by one micromort, and their associated cause of death: smoking 1.4 cigarettes (cancer, heart disease); drinking 0.5 liter of wine (cirrhosis of the liver); spending 1 hour in a coal mine (black lung disease); spending 3 hours in a coal mine (accident); living 2 days in New York or Boston (air pollution); living 2 months in Denver (cancer from cosmic radiation); living 2 months with a smoker (cancer, heart disease); drinking Miami water for 1 year (cancer from chloroform); living 5 years at the boundary of a nuclear power plant (cancer from radiation); living 150 years within 20 miles of a nuclear power plant (cancer from radiation); eating 100 charcoal-broiled steaks (cancer from benzopyrene); eating 40 tablespoons of peanut butter (liver cancer from Aflatoxin B); eating 1000 bananas, (cancer from radioactive 1 kBED of Potassium-40); travelling 6 minutes by canoe (accident); travelling 6 miles by motorbike (accident); travelling 17 miles by walking (accident); travelling 10 miles by bicycle (accident); travelling 230 miles by car (accident); travelling 6000 miles by train (accident); flying 1000 miles by jet (accident); flying 6000 miles by jet (cancer from cosmic radiation); and receiving one 10mrem chest X-ray in a good hospital (cancer from radiation). Increase in death risk for other activities on a per event basis: hang gliding – 8 micromorts per trip; scuba diving – 4.72 micromorts per dive; skydiving (in the US) – 17.5 micromorts per jump.

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